Components¶

class hermes.components.Component(notification_pipe, error_strategy, error_queue, backoff_limit=16)¶

Bases: hermes.log.LoggerMixin, multiprocessing.process.Process

A class which can be used to create both listener and processor objects. Callers must implement execute() and can others if they so choose.

The structure of calls:

  +-----------------+
  |      set_up     | <--------------+
  +-----------------+                |
           +                         |
           |                         |
           |                         |   ERROR
           V                         |
+-----------------------+            |
|      pre_execute      |            |
|        execute        | +----------+
|      post_execute     |
+-----------------------+
           +
           |
           |
           V
+-----------------------+
|      tear_down        |
+-----------------------+

The Component class adds a foundation for you to build a fully-fledged processor or listener. You can add/modify as much as you like - sensitive methods have been identified.

Parameters:	notification_pipe – The `Pipe`-like object to perform `select()` on. error_strategy – An object of type `AbstractErrorStrategy` to handle exceptions. error_queue – A `Queue`-like object to inform the `Client` through. backoff_limit – The maximum number of seconds to backoff a Component until it resets.

execute(pre_exec_value)¶

Must be overridden by callers. The return value will be passed to post_execute()

Parameters:	pre_exec_value – The value returned by `pre_execute()`

ident¶

Returns:	`ident()` unless the Component has not been started and returns None.

is_alive()¶

Returns:	`is_alive()` unless the Component has not been started and returns False.

join(**kwargs)¶

Returns:	`join()` unless the Component has not been started and returns immediately.

post_execute(exec_value)¶

Can be safely overridden by callers.

Parameters:	exec_value – The value returned by `execute()`

pre_execute()¶: Can be safely overridden by callers. The return value will be passed to execute().

run()¶

The main Component loop.

Callers should take great care when overriding.

set_up()¶

Called before execute methods and only once per iteration.

Overridden methods should call super.

start()¶: Initialises the process, sets it to daemonic and starts.

tear_down()¶

Called after execute methods and only once per iteration.

Can be used to tear down any resources.